The present disclosure relates to the compressed sensing of an electromagnetic environment using a Nyquist folding receiver (NYFR). It finds particular application in conjunction with the compressed sensing of a radio frequency (RF) environment using a NYFR and operatively associated antenna, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
Electronic intelligence (ELINT) is intelligence gathering using electronic sensors focused on RF signals-of-interest. Target signals vary wildly, ranging from radar, navigation beacons, jammers, radio control links, guidance systems, and identification friend or foe (IFF) systems (see R. Wiley, The interception and analysis of radar signals, 2nd ed. Norwood, Mass.: Artech House, 2006, pp. 1-8). Signals intelligence (SIGINT) is related to ELINT but is primarily focused on communication signals. These terms are often used interchangeably in electronic warfare (EW) literature. EW Receivers measure pulsed and low probability of intercept (LPI) signals and determine their carrier frequencies, pulse characteristics, phase or frequency variations, and polarization (see R. Wiley, The interception and analysis of radar signals, 2nd ed. Norwood, Mass.: Artech House, 2006, pp. 1-8.) The Nyquist folding receiver (NYFR) described herein is able to provide pulse rate, carrier frequency, phase variation, and frequency variation information while utilizing a compressed sensing methodology.
Wideband spectrum analysis of electromagnetic waveforms is constrained by many factors. Traditional receivers are limited by sampling speeds that must meet the Nyquist criterion and components with limited bandwidths, both of which prevent wideband interception of the radio frequency (RF) environment. The design, simulation, and prototyping of a photonic Nyquist folding receiver that alleviates many of the limiting factors that restrict current wideband signal collection are discussed in this thesis.
Prior work on Nyquist folding receivers has resulted in successful implementations of electrical receivers, but these are limited by their components in terms of bandwidth and sampling speed. This disclosure and the exemplary embodiments described herein addresses these concerns by developing a photonic compressed sensing receiver that takes advantage of advances in integrated optical components to sample and unfold wideband RF signals from the environment.
One motivation or benefit associated with the described exemplary embodiments is the application of compressed sensing techniques to a NYFR design implemented with wideband integrated optical components. Progress with photonic devices is rapidly surpassing conventional electronic systems. Digital EW receivers are taking advantage of these advances in order to digitize and process wide spectrum bandwidths. Specifically, optical receivers have an advantage in bandwidth, sampling speed, and immunity to electromagnetic interference. Photonic LiNbO3 modulators now have bandwidths on the order of 40 GHz and can efficiently couple RF-antenna signals directly into the optical domain (see K. Igarashi and K. Kikuchi, “Optical signal processing by phase modulation and subsequent spectral filtering aiming at applications to ultrafast optical communication systems,” IEEE Journal of Selected Topics in Quantum Electronics, vol. 14, no. 3, pp. 551-565, May 2008). Mode-locked lasers used for sampling now have tunable femtosecond-wide pulse widths with pulse-repetition frequencies (PRF) on the order of 300 GS/s to allow over sampling of complex modulations (see M. R. Arvizo, J. Calusdian, K. B. Hollinger, and P. E. Pace, “Robust symmetrical number system preprocessing for minimizing encoding errors in photonic analog-to-digital converters,” Optical Engineering, vol. 50, no. 8, 2011).